DESCRIPTION: This proposal is submitted in response to the program announcement PA-03-123 "Development of diagnostic screening test for salt sensitivity (SBIR/STTR)" from the National Institute of Diabetes and Digestive and Kidney Diseases. The overall hypothesis of our laboratory is the principle that NaCl homeostasis is maintained, in part, by an entero-renal endocrine axis in which renal NaCI excretion is rapidly regulated by uroguanylin (UGN) and guanytin (GN) to altered NaCI intake AND that these intestinally-derived peptides can fhodulate acute renal function in response to oral NaCi loads. It is well established in both humans and in experimental animals that orally-administered NaCI loads can be excreted more rapidly (within four hours) than equivalent salt loads administered intravenously, suggesting that an enteric factor may be capable of acute-regulation of renal function. Evidence from this and other laboratories suggests that UGN and GN are involved in and contribute to this response. However, methods to quantitatively and routinely determine the levels of UGN, GN, and their pro-hormones in biological fluids (i.e., serum, urine) have not been developed. Thus, lack of the reagents required for the quantitative assessment of these peptides has limited our knowledge of their role in pathologic conditions such as saltsensitive hypertension, congestive heart failure, and edema. To establish proof of principle, we will, in Aim 1, develop monoclonal antibodies to UGN to be used in a quantitative capture ELISA for murine UGN. In Aim 2, we will validate this ELISA in a mouse model developed in our laboratory in which the renal response and the serum and urinary levels of UGN will be measured prior to and after (1) intravenous doses of UGN and (2) intra-gastric (oral) salt loading; UGN wiH be measured by ELISA and confirmed by HPLC and Western blotting. We predict that the development of this quantitative ELISA will allow us to determme the rote of guanylin peptides in the acute renal response to oral NaCI loading.